The equal tempered tuning of today's chromatic electronic and digital instruments is a compromise that the evolution of Western music has produced to allow chromatic instruments with fixed tuning to play music that progresses through many keys, modulating from one harmony to another. This is done by allowing all notes of the instrument to be very slightly out of tune. This type of tuning of a chromatic instrument is at one end of a spectrum, where at the other end we find the just tuning, where the intervals are based on the harmonics of the root of the key. The just tuning will sound at its best in the key which root it has been tuned after. The further away you modulate in the circle of fifths from this key, the more out of tune the tuning will be. Several fixed tuning systems with characteristics between the just tuning and the equal tempered tuning exist. Gannon U.S. Pat. No. 5,501,130 offers an historical treatment of static tuning systems.
Electronic and digital technology has made it possible to manipulate the fixed tuning of a chromatic equal tempered instrument to allow flexible intonation depending on the melodic and harmonic contents of the music. It has been considered desirable to come closer to a just tuning for the key the music is performed in. Mohrlok U.S. Pat. No. 5,442,129 describes a method of achieving a just tuning by comparing played notes to chord patterns arranged in tables. Clynes U.S. Pat. No. 6,924,426 describes a method of achieving an automatic expressive tuning by pitch adjustment determined by the interval of two consecutively played notes, without regard to the harmonic context. None of these methods offers a way to provide an intonation consistent with the practices developed by orchestral musicians when performing Western music.
Shibukawa U.S. Pat. No. 5,220,122 A describes an “Automatic accompaniment device with chord note adjustment” that can identify chords “to generate accompaniment tones in conformity with the detected tonality.” Okuda et al. U.S. Pat. No. 5,302,777 describes a “Music apparatus for determining tonality from chord progression for improved accompaniment” that will determine tonality of music by examining the input chords. Tanaka U.S. Pat. No. 6,002,080 A describes an “Electronic wind instrument capable of diversified performance expression” which provides a “plurality of keys for designating a pitch and a plurality of sensors for detecting operating states of the keys.”